Hidden Artifacts (continued)
The upshot is that most modern audio measurement systems and the engineers that design them place far greater emphasis on identifying the more obvious and offensive problems that tend to plague all audio components while dismissing the "not so obvious" ones as relatively inconsequential. That does make good sense as a first-order approach because similarly, we would want our doctor to check us for major diseases first before worrying about a pimple on our butts. Then again, even though most of us can easily overlook it, a pimple on the butt of a beautiful swimsuit model posing in the nude can just about ruin the photographer's shot (and it would were it not for skillful touch-ups of an airbrush artist). It's all a matter of perspective, and assuming the audio manufacturer has done his job we shouldn't even have to worry about our audio gear having any major "diseases." No... it's all about the pimples and how they distract us from an otherwise beautiful thing - butts, music... or whatever :-))
Therefore, as you may have guessed by now it all has to do with the spectral content and general makeup of the very low-level information residing within the realm of the component's noise floor (i.e., its "bottom-end" :-). At those levels it can become virtually impossible for even the most advanced test equipment to differentiate between the original signal, distortion artifacts and random electrical noise. That's why you see the "THD + Noise" specification being tossed around so much. They just lump it all together and call it "good." Because of the inherent limitations of the test equipment and/or test algorithm there is no way to really know which is which. At such low levels it actually takes the ALMOST INFINITE PROCESSING POWER OF A HUMAN BRAIN (i.e., advanced intelligent filtering) to differentiate between what is genuine low-level audio detail vs. signal-related distortion artifacts vs. plain old "random noise."
Yes,... it's extra nice when the "bottom end" is as pretty as the top, whether it be in relation to audio gear or otherwise. Notwithstanding, no "stupid" man-made machine can tell the difference between "pretty" and "ugly" when everything is mixed together like it is way down at the very bottom-end of an audio component's dynamic range. Just *maybe* that's one of the many reasons God invented ears in the first place, eh?!!!